This invention relates generally to metal-gas cell batteries, such as metal-air cell batteries, and, more particularly, to mechanically rechargeable metal-air cell batteries.
More powerful, longer-lasting batteries are a high priority item for all countries seeking to replace hydrocarbon fueled vehicles with smogless electrically powered vehicles. In this regard, a great deal of research is presently focused on metal-gas cell batteries, such as zinc-air batteries. Zinc-air batteries have among the highest theoretical specific energy content of all known battery types. Many problems, however, must be overcome before vehicles powered by zinc-air batteries are regarded as acceptable alternatives to hydrocarbon burning vehicles.
All metal-gas cell batteries comprise a plurality of cells wherein each cell has at least one gas-diffusion cathode and a metallic anode separated by a quantity of alkaline electrolyte and some form of mechanical separation sheet. In the operation of metal-gas cell batteries, a reactant gas, such as oxygen, reacts at each gas-diffusion cathode to form anions. At each anode, the anions react with metallic anode material. The process creates an electrical potential between each cathode and each anode. When the cells are connected in series, the combined electrical potential of all of the cells can be considerable, and can be used as a source of electrical power. As can be seen, however, the operation of the battery gradually depletes the available metallic anode material and the battery has to be periodically recharged.
Metal-gas cell batteries can be recharged either electrically or mechanically. Electrical recharging can be easily adapted to existing power networks, but electrically rechargeable batteries have a markedly limited service life. Moreover, an electrically rechargeable metal-gas battery requires a bi-functional or additional gas diffusion electrode. Having to use such a bi-functional or additional gas diffusion electrode requires that the battery be unduly heavy, bulky and complicated.
Accordingly, the recharging mode of choice for metal-gas cell batteries is presently mechanical refueling, whereby the spent metallic anode is physically replaced with a fresh anode. Mechanical refueling can be accomplished in two ways. In a first way, the metallic anode comprises metallic pellets or powder suspended within the electrolyte. When the metallic pellets or powder becomes spent, the metallic pellets or powder is pumped from the cell and fresh pellets or powder is pumped into the cell. U.S. Pat. Nos. 3,981,747, 5,006,424, 5,434,020 and 5,558,947 disclose attempts to use zinc particles or pellets as anodes.
The second way of mechanically refueling a metal-gas battery is far simpler than the first way. In the second way, the metallic anode is a rigid structure. When the metallic anode becomes spent, the anode is removed and a replacement anode is reinstalled into the cell. Because of its simplicity in theory, construction, maintenance and operation, the second of the two refueling methods is generally employed. U.S. Pat. Nos. 3,513,030, 5,203,526, 5,318,861, 5,366,822, 5,418,080, 5,447,805, 5,753,384, 5,904,999 and 6,057,053 all disclose various methods of mechanically refueling metal-gas cell batteries by changing out a rigid anode structure. Each of the patents listed in the immediately previous sentence are incorporated herein by this reference in their entireties.
One problem with such prior art metal-gas cell batteries is the difficulty with which the rigid anode structures are removed from the cell and inserted into the cell. In a conventional cell where the supporting structure is wholly rigid, clearances for the removal and reinsertion of such anodes are generally very small. The gas cathodes and separator sheets are often abraded during the removal and reinsertion of the anodes. U.S. Pat. Nos. 4,389,466 and 4,560,626 disclose an attempt to solve this problem. However, the total contact area between the cone-shaped current collectors and the metallic anodes used in the batteries disclosed in these patents is not sufficient for large currents. Moreover, pinpoints on the current collectors in the batteries disclosed in these patents often make the insertion and extraction of the metallic anodes very difficult. Another attempt to solve this problem is disclosed in U.S. Pat. No. 5,286,578. In this patent, it is suggested to make a metal-gas cell battery with a wholly flexible housing. However, such housing is fragile and cannot withstand repeated refueling. Other wholly flexible housing systems are disclosed in U.S. Pat. Nos. 5,415,949 and 5,650,241. Such housing systems are unduly complex and are therefore expensive to manufacture, maintain and operate.
U.S. Pat. Nos. 4,389,466 and 4,560,626 disclose using neoprene as the material to make a soft pocket. Although neoprene is well known in the art as the most alkaline-resistant rubber, due to the elasticity of the neoprene a soft pocket made with neoprene will be heavily deformed, just like a rubber balloon filled with water. This will result in fatigue of a neoprene-made soft pocket too early in the later refueling process.
U.S. Pat. No. 5,286,578 discloses a collapsible electrochemical cell using xe2x80x9ca flexible plastic materialxe2x80x9d to satisfy its collapsible design. No detail of the flexible plastic material was disclosed, however. Similarly, U.S. Pat. No. 5,415,949 suggests using a pouch cathode, but no teaching is given on how to make the pouch.
Another problem with metal-air cell batteries, which are mechanically refueled by physical replacement of a rigid anode structure is the frequent leakage of the alkaline electrolyte. In most prior art designs, the housing of the metal-gas cell is usually opened at the top. The opening is sealed during operation by some form of elastic sealing element disposed between the cell housing and a protruding portion of the anode assembly. This protruding portion of the anode assembly is universally used in such designs for electrical connection to battery electrodes. Moreover, it is common to provide one or two small breathing holes along the uppermost portion of the cell proximate to the protruding portion of the anode. However, alkaline solution tends to creep up the anode and out of the cell along the protruding portion of the anode. Also, alkaline mist continuously escapes through the breathing holes. Such leakage and mist can cause rapid oxidation of the conductors above the anode and the air cathode. Oxidation dramatically increases the electrical resistance between the contacted surfaces and therefore results in a marked loss of battery power. Moreover, the continuing leaking of alkaline electrolyte and electrolyte mist makes the battery difficult to use in any kind of environment where oxidation of metallic items outside of the battery is a problem. Finally, any upset of the battery during handling or operation will cause copious leakage of electrolyte out of the battery.
Accordingly, there is a need for a metal-gas cell battery which is conveniently rechargeable by mechanical replacement of anode material and which avoids the aforementioned problems in the prior art.
The invention satisfies this need. The invention is a metal-gas cell storage battery comprising at least one battery cell. Each battery cell comprises (i) a first gas cathode disposed within a rigid planar first retaining structure, the first gas cathode being permeable to air but impermeable to liquids, the first gas cathode allowing the passage of gases into the cell, (ii) a second gas cathode disposed within a rigid planar second retaining structure, the second gas cathode being permeable to air but impermeable to liquids, the second gas cathode allowing the passage of gases into the cell, the second retaining structure being moveable with respect to the first retaining structure between a first retaining structure position wherein the first retaining structure is proximate to the second retaining structure and a second retaining structure position wherein the first retaining structure is spaced apart from the second retaining structure, the second gas cathode being electrically connected to the first gas cathode, (iii) a soft pocket disposed between the first gas cathode and the second gas cathode, the soft pocket having a flexible and planar first wall and a flexible and planar second wall, the first wall having a periphery and a central opening, the periphery of the first wall including a top edge, the second wall having a periphery and a central opening, the periphery of the second wall including a top edge, the periphery of the first wall connected to the periphery of the second wall except along the respective top edges, the periphery of the first wall being attached to the first retaining structure and the periphery of the second wall being attached to the second retaining structure, whereby the first retaining structure, the first gas cathode, the first wall, the second wall, the second retaining structure and the second gas cathode cooperate to define a liquid retaining soft pocket chamber having a soft pocket lower portion, a soft pocket upper portion and a soft pocket top opening defined between the top edges of the first and second walls, the soft pocket top opening being open in the second retaining structure position and tightly closed in the first retaining structure position, (iv) a soft pocket closing mechanism for securing the first and second retaining structures in the first retaining structure position, and (v) a metallic anode disposed within the soft pocket chamber.
The cell further comprises a positive first battery positive terminal electrically connected to the two gas cathodes and a negative second battery negative terminal electrically connected to the metallic anode.
In a typical embodiment of the invention, the gas cathode is an air cathode and the metallic anode is comprised substantially of metallic zinc.
In a preferred embodiment of the invention, the metallic anode is wholly disposed within the soft pocket chamber.
In another embodiment of the invention, the battery further comprises a second semi-permeable membrane disposed within the upper portion of the soft pocket chamber to reduce the pressure difference between the soft pocket chamber and the outside atmosphere.
In another embodiment of the invention, the soft pocket is made of a fabric reinforced membrane, such as vinylon or nylon fabric coated on one or both sides with neoprene, or of polypropylene or polyethylene with coating on one side of polypropylene or polyethylene, or of polypropylene or polyethylene with coating on a first side of polypropylene or polyethylene, and a coating on a second side of PVC. The fabric may be alkaline-resistant and selected from the group consisting of vinylon, nylon, polypropylene, polyethylene, ethylene propylene diene monomer, butyl rubber, ethylene-propylene copolymer, and chlorosulfonated polyethylene.
In a typical embodiment, the soft pocket closing mechanism is provided by one or more straps which circumscribe the one or more cells. Optionally, the soft pocket closing mechanism comprises one or more than one bolt and one or more than one nut. In one embodiment the soft pocket is comprises a molded integral piece w-shaped in cross section.
In a further embodiment of the invention, the periphery of the first wall is attached to the first retaining structure and the periphery of the second wall is attached to the second retaining structure, by mechanical force without glue.
The invention provides a metal-gas cell battery, such as a zinc-air battery, which is suitable for rapid refueling and which is sufficiently durable for hundreds of refueling operations. The invention also provides a metal-gas cell battery which does not leak electrolyte or electrolyte mist.